Explosion vents and doors are frequently installed in silos, hoppers, bins, dryers and other large chambers for handling of bulk materials, that can potentially experience a destructive explosion. In order to prevent damage or destruction to the structure and the accompanying safety hazards and financial losses, an explosion vent or door is installed to vent the expanding gases during the explosion. Typically the vent or door is secured and sealed during normal operation of the chamber, and opens only in the event of a sudden increase in pressure such as an explosion. A typical explosion door comprises a frame for mounting within a corresponding opening within the wall of the chamber. A door panel is releasably secured to the frame. In one type of explosion door, the door panel is held against the frame by a releasable latch which retains the door in the shut position during normal operation of the chamber. A seal between the door and the chamber is provided.
The latch permits the door to burst open in the event of a sudden increase in internal pressure within the chamber, indicative of an explosion. Conveniently, adjustable means are provided to permit the user to adjust the securing means to permit the door to open at a selected burst pressure. Typically, the latch permits the door to open at a selected pressure in the range of a 0.5-2.0 psig. The area of the door should be large enough to vent the enclosure sufficiently to limit structural damage.
Conventional latch-type explosion door systems typically include a retainer bar spanning the frame and spaced apart from the outer face of the door panel. The bar is hinged at one end to a first side of the frame and at the other end is latched with a releaseable latch to the opposing side of the frame. Release of the bar from the latch permits the door to open. An array of springs or other biasing means between the bar and the door panel retains the door in the shut position. Conveniently, the biasing means are adjustable. The latch is actuated by a an actuator rod between the door and the latch whereby when sufficient pressure acts outwardly on the door to counteract the biasing means such that the door partly opens, the latch is released and the door is permitted to fully open to permit the release of the excess gas pressure.
The latch structure of the prior art devices typically comprises an elongate latch housing hinged at one end to the retainer bar and engaging a frame member (as seen in FIG. 1(a) and 1(b), with the opposing end extending when the latch is in the closed position towards the opposing frame member. The latch housing incorporates a magnet stop bar, which in turn is hinged to the interior of the latch housing, for magnetic contact with a magnet mounted to the retainer bar. The hinged connection between the magnetic stop bar and the latch housing is required in order to permit the exposed flat face of the magnetic bar to make a solid, parallel contact with the stop member Typically, the actuator rod contacts the latch housing at a position between the magnetic bar and the latch housing hinge. The length of the actuator rod is adjustable to reflect the spacing between the retainer bar and the door panel, which in turn permits adjustment of the burst pressure required to open the door.
A drawback of the conventional latch mechanism described above resides in the difficulty of opening and closing the latch as a result of uneven contact between the retainer bar and the hinged magnetic bar. Further, the hinged member renders difficult the making of a consistently solid contact between the latch housing and the retainer bar.
In a further aspect of the conventional devices, the seal between the door and the housing comprises a an extrusion having a U-shaped profile, the flanges of which mount to the inner and outer faces, respectively, of the door panel. A flexible and resilient seal member is attached to the exterior of the extrusion for contact with the frame. This arrangement is relatively costly to manufacture, and as well potentially permits leakage between the inner flange and the door panel. Accordingly, it is desirable to provide a seal wherein these drawbacks are addressed.
A further aspect of the prior art explosion doors resides in the means by which the actuator rod is mounted to the door. In the prior art, this component is bolted to the door panel, by means of a bolt that extends through the door panel. The resulting opening through the panel impairs the integrity of the door panel. Accordingly, it is desirable to provide an explosion door having an minimum of intrusions extending in through the door into the interior of the chamber.